Currently, with the development of smart phones, mobile phones have become an important part in people's life. Phone calls also have become one of the important communication manners for people. Smart phones often run out of power, due to its limited battery capacity. If a mobile phone is running out of power or shut down, the mobile phone cannot receive calls, and thus some important calls may be missed. As a result, a user cannot be inform of in time whether someone has called the user during the shutdown or under other conditions that the phone is not available.